The invention relates to a guiding device for a drilling device as well as to a drilling device having such a guiding device
From the state of the art drilling devices are known, with which a change of drilling direction during the drilling of the borehole is possible.
For example from the field of horizontal drilling technology, drilling devices are known, in which a drill head, which is connected via a drill rod to a drive unit located above ground, is propelled statically and/or dynamically into the soil by the drive unit. A steering function can be achieved in such drilling devices by providing the drill head with an asymmetrically slanted face surface to cause a lateral force to act on the drill head when being advanced through the soil, leading to a deviation of the drill head from the straight drilling direction. Advancing such a slanted drill head only statically or dynamically without rotating leads to an arched course of the drill inside the soil. Such a drilling device enables a straight drilling by advancing the slanted drill head not only under pressure but at the same time driven rotatingly so that lateral forces which cause a deviation are compensated over the course of a complete revolution of the slanted drill head and on average a straight drilling course results.
Such Drilling devices are suited well for a drilling in soils, which can be easily deformed because the drilling effect is essentially based on a radial displacement and compaction of the soil. Such drilling devices are, however, inadequate for use in a harder soil and in rock formation, because here it is necessary to first break down and then remove the rock from the borehole.
Essentially, two different designs of drilling devices exist, which are suitable for drilling in harder soil as well as in rock formation.
Drilling devices according to a first of these designs are based on an in-hole motor, i.e. a motor which is arranged in the region of the drill head of a drilling device and, together with the drill head, is propelled through the soil. The in-hole motor acts directly on and rotatingly drives the drill head. The pressure forces necessary for the propulsion of the drill head are transferred to the drill unit, comprised of the in-hole motor and the drill head, via a drill rod by a drive unit which is located above ground. So-called “mud-motors” are normally used as in-hole motors. These involve motors which operate according to the “Moineau”-principle or are based on turbines and driven hydraulically. The mud-motors are typically driven by a drilling fluid which is fed to the mud-motors under high pressure through the hollow drill rod or other feed pipe, after which the drilling fluid is discharged via respective outlet openings in the region of the drill head, to lubricate and cool the front of the drill head and to flush out the removed soil or rocks from the borehole.
A steering ability in this type of drilling devices can be achieved in that the housing of the in-hole motor, which is preferably located as close as possible to the drill head or a section of the rod assembly, is provided with deflection means, which generate a lateral force causing a respective deviation from the straight drilling course.
From the state of the art, it is known to use a so called deflection shoe as deflection means, which deflection shoe is fastened to one side of the housing of the in-hole motor or a section of the drill rod and thus causes the lateral deflection. As an alternative, the same effect can be achieved by forming the housing of the in-hole motor or a section of the drill rod asymmetrically. A third known possibility is to provide the housing of the in-hole motor or a section of the drill rod with a curvature or an angled course to achieve the desired deflection. Further, it is known to connect the drill head itself to a driveshaft of the in-hole motor such that the rotation axis of the drill head is not coaxial to the longitudinal axis of the in-hole motor and the section of the drill rod which is connected to it. A straight drilling course is achieved with these drilling devices by rotatingly driving the housing of the in-hole motor which comprises the deflection means and the rod assembly so that the lateral force action of the deflection means is compensated over the course of a complete revolution. For changing the drilling direction, the rotation of the housing and the drill rod is interrupted however until the desired drilling direction is achieved.
These drilling devices have the disadvantage that they require large amounts of drilling fluid under high pressure for driving the mud-motors, and therefore require the provision of large and expensive pumps. Also, a sufficiently great cross section has to be provided inside of the drill rod through which the drilling fluid can be transported to the mud-motor by a pump located at the surface, to prevent the flow resistances inside the drill rod from causing excessive pressure loss. With regard to the forces and torques that have to be transferred, the drill rod therefore has to be “overdimensioned”. A further problem is that the disposal of the spent drilling fluid is elaborate and therefore expensive. Because significantly more drilling fluid is required for driving the mud-motors than would be needed for cooling, lubricating and flushing out the drillings, the cost of disposal of the drilling fluid also rises.
These drawbacks of drilling devices based on in-hole motors for hard soil and rock formation have led to the development of drilling devices that are independent of such an in-hole motor, but are still suitable for a drilling in hard soil or rock formation. These drilling devices are based on a double drill rod which includes an outer tube having a front end which faces the drilling ground and is normally provided with a ring-shaped annular bit, and an inner rod assembly which is rotatably supported inside the outer tube and has a front end on which the actual drill head is disposed. The double drill rod is advanced rotatingly as well as under pressure by a drive unit which is located above ground. Normally, the outer tube and the inner rod assembly are advanced in synchronism, while rotatingly driving the outer tube and the inner rod assembly independent of each other. The inner rod assembly is here driven with a rotational speed which is configured to achieve a most optimal removal of soil or rock. The outer tube which because of its direct contact with the inner wall of the already created borehole is subjected to significant friction with the inner wall is normally driven with lower rotational speeds to keep friction losses and resulting wear as low as possible.
The rotation of the outer tube rather has merely the purpose to achieve the desired steering function of the drilling device. For this, similar to the drilling devices with in-hole motor, the outer tube of the double rod assembly is provided with deflection means in the region of the drill head to generate a lateral force, causing an arched drilling course when a non-rotating outer tube is involved. For a straight drilling, the outer tube is rotated continuously according to the same principle as in the afore-mentioned alternative drilling devices so that on average a straight drilling course is established. The rotational speed of the outer tube which for this purpose rotates continuously can be significantly lower than a rotational speed that is appropriate for the inner rod assembly which carries the drill head. The major disadvantage of such devices with double drill rod is the elaborate and therefore expensive construction of the double drill rod itself.
Against the background of this state of the art, the invention was based on the object to provide a drilling device which is simple in structure and makes it possible to introduce boreholes in hard soil or rock formation.